The current round of Sino-Japanese tensions may have been triggered last April when the then-governor of Tokyo announced plans to buy the Diaoyus/Senkakus, but Japanese defence analysts believe Beijing was plotting a diplomatic assault on the sovereignty of the islands.

Japan's National Institutes of Defence Studies (NIDS) released its annual East Asian Strategic Review early today, analysing changes in the security environment over the past 12 months.

China, inevitably, accounts for a large percentage of the complete report, including discussion of how political changes in Beijing are likely to affect its foreign and security policies. However, the study lingers on what are termed "increasingly strained relations with Japan".

"China reacted furiously to governor of Tokyo Shintaro Ishihara's announcement on April 16 of his prefecture's proposal to buy the islands and to the Japanese government's decision on September 11 to purchase three of the islands," the report said.

"However, there had been signs of the rising tension even before Ishihara's plan.

"The actions that China subsequently took clearly reveal that it was already meticulously planning measures for advancing its claim over the Senkakus from a very early stage," the report said. "China has used the same approach with regard to the South China Sea and shows no hesitation in carrying out actions that cause friction with neighbours."

Dr Eiichi Katahara, director of the Regional Studies Department of the NIDS, which is affiliated with Japan's Defence Ministry, said Japan's responses throughout the ongoing dispute had been measured and appropriate.

"The Japanese government's stance is that long-term, strategically mutual relations will benefit both sides and they want to make sure individual issues do not ruin the overall relationship," he said.

The Japanese government's stance is that long-term, strategically mutual relations will benefit both sides and they want to make sure individual issues do not ruin the overall relationship

Issues such as containing the threat posed by North Korea fall into this category, he said, and should be dealt with "appropriately". "But Japan is taking a calm and determined stance on the Senkakus, while at the same time trying to maintain good communications with China and asking Beijing to restrain itself," he said.

Katahara also believed dialogue between the two nations' leaders could lead to a resolution of many of the problems that bedevil the relationship. He said the efforts Prime Minister Shinzo Abe made to improve ties the last time he was leader of Japan, in 2007, meant that Beijing may be anticipating some sort of "breakthrough in bilateral relations".

The report touched on suggestions China is attempting to build closer relations with Russia and to access advanced technology, mentioning the recently reported deal to buy Sukhoi-35 fighters. But an NIDS analyst suggested that Moscow's agreement to it was far off, with Russia more wary of China's ambitions.

North Korea also took up a large part of the annual study.

Hiroyasu Akutsu, a North Korea analyst at the institute, said while Beijing appears to be taking a "strict stance" with Pyongyang over its recent missile and nuclear tests, there was no guarantee that would last.

"China has acted strictly in the past, such as in 2009 when North Korea carried out a missile launch and its second nuclear test," he said. "China at that time signed resolution 1874 in the United Nations Security Council, but five months later it was back supporting North Korea again.

"For China, the top priority is the stability of the region and they do not want to take any actions that will lead to the collapse of North Korea, so they are being very careful."

This article appeared in the South China Morning Post print edition as China 'planned diplomatic assault'